FIG. 10 is a cross-sectional view of a thermal print head as an example of a known liquid discharge head. In FIG. 10, the print head includes an ink feed member 2 and a chip 1 bonded on the ink feed member 2. The chip 1 includes heater elements 3 disposed on a semiconductor substrate 1a; and a coating layer 4 disposed so as to position nozzles 4a above the respective heater elements 3. An individual channel 4b extends from regions above the heater elements 3 to a periphery region communicating with the regions above the heater elements 3. Furthermore, the semiconductor substrate 1a includes a through hole 1b. 
On the other hand, the ink feed member 2 includes an ink feed opening 2a and a common channel 2b through the base of the ink feed member 2, the common channel 2b communicating with the ink feed opening 2a. 
In the print heat, ink is fed from an external ink tank (not shown) or the like into the common channel 2b through the ink feed opening 2a. The ink enters the individual channel 4b through the through hole 1b. As a result, the regions above the heater elements 3 are filled with the ink.
Rapid heating of the heater elements 3 in this state generates bubbles on the heater elements 3. A change in pressure during the generation of the bubbles discharges the droplet of ink above the heater elements 3 through the nozzles 4a. The discharged ink reaches a recording medium or the like to form a pixel.
The print head is produced as described below.
First, the heater elements 3 are formed by semiconductor production techniques or the like on a substrate (semiconductor substrate 1a) composed of, for example, silicon. A pattern composed of a soluble resin, e.g. a photosensitive resin such as a photoresist is formed by photolithographic techniques on the heater elements 3 to form a sacrificial layer (not shown). The coating layer (resin layer) 4 to be a structure is formed on the sacrificial layer by application such as spin coating.
The nozzles 4a are formed by dry etching in the coating layer 4. When the coating layer 4 is composed of a photosensitive resin, the nozzles 4a are formed by a photolithographic technique. The through hole 1b serving as the ink feed opening 2a is formed by wet etching from the back side of the semiconductor substrate 1a as described in, for example, Japanese Patent No. 3343875. A dissolving liquid for the sacrificial layer is poured through the through hole 1b. When the sacrificial layer is composed of a photosensitive resin, a developer or the like is poured through the through hole 1b. Thereby, the sacrificial layer is dissolved (eluted) to form the chip 1.
The ink feed member 2 is composed of aluminum, stainless steel, or a resin and is formed by machining. The chip 1 is bonded to the ink feed member 2. Thereby, a print head is completed.
In the known technique, the through hole 1b is formed in the semiconductor substrate 1a from the back side of the semiconductor substrate 1a. The dissolving liquid for the sacrificial layer is poured through the through hole 1b to dissolve the sacrificial layer. The step of forming the through hole 1b in the semiconductor substrate 1a is usually performed by either anisotropic wet etching or dry etching, or a combination of both.
However, anisotropy etching has disadvantages as described below.
First, the etch rate is very low (about 0.5 to about 1.0 μm/min). For example, the time required for forming the through hole 1b in the semiconductor substrate 1a having a thickness of about 600 μm is at least about 10 hours. Thus, it disadvantageously takes a very long production time.
Secondly, a member functioning as an etching mask needs to be formed in a region other than the through hole 1b before forming the through hole 1b, thus disadvantageously complicating the process.
Thirdly, in the case where an aluminum pad or the like is disposed on a surface of the semiconductor substrate 1a, when an etching solution reaches the surface, the aluminum pad is disadvantageously etched. Thus, it is necessary to prevent the etching solution from reaching the surface. Alternatively, it is necessary to form a protective film so as not to cause a problem even when the etching solution reaches the surface.
On the other hand, dry etching also has disadvantages as described below.
First, the etch rate is disadvantageously lower than that in anisotropic etching.
Secondly, an etching mask is disadvantageously required in the same way as the second problem in anisotropic etching.
As described above, the use of etching techniques complicates the production process and prolongs the production time. Thus, the print head has poor yield, resulting in high costs.